If we want to find all cars over $10,000 and also calculate the average price for those cars, we can simply use a filtered query:

GET /cars/transactions/_search?search_type=count
{
    "query" : {
        "filtered": {
            "filter": {
                "range": {
                    "price": {
                        "gte": 10000
                    }
                }
            }
        }
    },
    "aggs" : {
        "single_avg_price": {
            "avg" : { "field" : "price" }
        }
    }
}

Fundamentally, using a filtered query is no different from using a match query, as we discussed in the previous chapter. The query (which happens to include a filter) returns a certain subset of documents, and the aggregation operates on those documents.